Abscisic acid (ABA) is a plant hormone that is derived from carotenoids. ABA triggers a number of plant responses including seed dormancy, maturation, germination and adaptive responses to drought stresses. My research team performed molecular genetics and functional genomics research and revealed some novel mechanisms of ABA-mediated transcription in seeds and of dynamic regulations of ABA biosynthesis and catabolism. Our analysis indicates that vascular parenchyma cells play a central role in ABA biosynthesis, whereas ABA catabolism is activated locally in various cell types suggestive of a link to its signaling pathway.

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Flowers emit floral scent compounds throughout the initial unfurling till the senescence stages. Floral scent compounds serve as attractants for species-specific pollinators. Recent progress in elucidating the biosynthetic pathways, enzymes, and genes involved in the formation of floral scent compounds allowed the determination of their physiology and function rigorously investigated at the molecular and biochemical levels. We investigated the biosynthesis and the emission of floral scent compounds in the flowers of roses and Osmanthus flowers. During the course of our research, we employed feeding experiments of stable isotopes and investigated the biosynthetic pathways based on the molecular biological methodologies. In this paper, 1) We describe the involvement of 2-phenylethylβ-D-glucopyranoside in the emission of 2-phenylethaol in rose flowers. 2) Moreover, we have elucidated that 2-pheylethanol emitted from rose flowers was synthesized from L-phenylalanine by the action of two enzymes, an aromatic amino acid-decarboxylase and a phenylacetaldehyde reductase. 3) We have also observed the seasonal change in the biosynthetic pathways of 2-phenylethanol in the roses. 4) Furthermore, we have characterized o-Methyl transferase as one of the key enzymes involved in the formation of floral scent methoxy-phenol in Chinese roses. 5) We have also confirmed that CCD1 was clarified to be involved in the synthesis and rhythmic emission of α-, β-ionones from carotenoids in Osmanthus flowers grown under the 12h light-12h dark conditions.

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Analysis of gibberellin (GA)-deficient dwarf mutants contributed to the identification of GA biosynthesis genes. Meanwhile, additional GA-related genes that have not been discovered by conventional forward genetic approach are likely to be present. We identified such genes by analysis of an activation tagged mutant (1), and by reverse genetic approach (2). (1) A dominant dwarf mutant designated dwarf and delayed-flowering1 (ddf1) was isolated from a library of activation-tagged Arabidopsis. Genetic and molecular analyses revealed that the ddf1 phenotypes are caused by increased expression of GA2-oxidase7 gene (GA2ox7), which encodes a C20-GA inactivation enzyme, through increased expression of a high salinity responsive AP2 transcription factor, DDF1. (2) A rice P450 gene, EUI (CYP714D1) encodes a novel class of GA inactivation enzyme. We examined the possible involvement of other CYP714 members of Arabidopsis and rice in GA metabolism. We found the gene products that have GA13-hydroxylation activity from Arabidopsis (one gene) and rice (two genes). GA measurements of a rice double mutant of these genes indicated that the levels of 13-hydroxy GAs were decreased, whereas those of non 13-hydroxy GAs were increased in the double mutants. These results strongly suggest that these two cytochrome P450 genes play a major role in GA13-hydroxylation in rice.

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Holoparasitic plants such as Orobanche spp. have lost their photosynthetic ability. On the other hand, hemiparasites retain photosynthetic ability. In the holoparasitic species, selective pressure to maintain photosynthetic ability had been released. Photoresponses of plants which are important to optimize photosynthesis for green plants are not necessary in holoparasites. Photoresponses are also involved in the regulation of plant development such as germination process. Studies on photoresponses of parasitic plants revealed that the pattern of their photoresponses had been modified for adaptation to its parasitic life cycle. Molecular analysis of their photoreceptors also demonstrated that the alteration of amino acid sequences and associated molecular function. Elucidation of altered components in these parasitic plants will provide useful information not only about its physiological characteristics but also about general plant photoreception systems and evolution.

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When damaged by herbivorous arthropods, plants are known to emit a blend of volatiles that have several ecological functions in nature. One of the well known functions is to attract carnivorous natural enemies of inflicting herbivores. Volatiles from infested plants are specific in terms of herbivore species and plant species. The carnivores are known to cope with such specificity by learning. The first part of this paper will show the learning behavior of parasitic wasps that attack aphids on bean plants. In the second part of this paper, we will focus on the multifunctional aspects of volatiles from plants that are either infested or intact. Our recent results on the tritrophic interaction of willow plants, willow leaf beetles and ladybirds showed that the volatiles from willow plants infested by leaf beetles mediated interactions between plants and leaf beetles, plants and ladybirds. Further, these interactions were affected by their physiological conditions, gender and developmental stages. Based on these data, we will discuss the interaction and information networks mediated by ecological volatiles.

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A pre-infestation of the white-backed planthopper (WBPH), Sogatella furcifera Horvath, conferred resistance to bacterial blight disease and rice blast disease in rice under both laboratory and field conditions. The infestation of another planthopper species, the brown planthopper (BPH) Nilaparvata lugens Stal, did not significantly reduce the incidence of bacterial blight symptoms. A large-scale analysis using a rice DNA microarray revealed that WBPH infestation caused the upregulation of more defence-related genes than did BPH infestation. One C_6 antibacterial volatile, (E)-2-hexenal, accumulated in rice after WBPH infestation but not after BPH infestation. Based on these data, we conclude that plant volatiles play some role in WBPH-induced resistance in rice.

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Ecological volatiles play important roles in plant reproduction and insect foraging. In particular, chemoecological interactions between flowers and eusocial bees form the coevolutionary basis of improved fitness for both plants and bees. It is well known that eusocial bees evaluate flowers offering good rewards by using floral scents as olfactory cues. Although flowers emit various volatiles to attract bees, we do not know their ecological function. This paper describes some research on the functional meaning of ecological volatiles in eusocial bees (Apis and Bombus spp.), hornets (Vespa spp.), and plants. Volatiles emitted by many plant species contain pheromonal components of potential pollinators. Plants emit two types of volatiles: 1. A component (same and/or similar to pheromonal component) that is innately attractive to even naive bees; and 2. Species-specific floral scents that cause learned association with rewards, such as nectar and pollen. The interaction is mutually beneficial to both plants and pollinators. Practical use of an ecological volatile to improve crop pollination by honeybees is introduced.

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Plants show a broad diversity of defense strategies against a wide range of pests. Both constitutively and inducibly in response to biotic stresses, plants release volatile organic compounds including a wide-range dynamic chemical array of terpenoids (terpenes). Terpenes in terrestrial environments are known to function as airborne signals to communicate with other land-living organisms, e.g., insects, bacteria and plants. These chemical compounds, in organisms ranging from algae to higher plants, are biosynthesized via two biosynthetic pathways: the mevalonate pathway and the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway connecting to a large diversity of synthetic and modification enzymes including terpene synthases and cytochrome P450 monooxygenases. Moreover, in terrestrial ecosystems, since the blends of terpenes may vary with the attacking herbivore, various components and crosstalk between the involved signaling pathways are thought to be responsible for the characteristic terpene blend. These specific blends of terpenes provide the majority of constitutive and induced chemical defense systems and serve for attracting carnivorous natural enemies of the herbivores, thus resulting in the removal of herbivorous arthropods from a wide array of plant species. Implications for the nature, biosynthesis and regulation of terpenes in both angiosperms and gymnosperms are discussed.

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This article deals with the effects of olfactory stimulation with grapefruit oil, lavender oil and other essential oils on body funtions. It was observed that stimulation with scent of grapefruit oil activated the sympathetic nerve innervating the white adipose tissue, brown adipose tissue, adrenal gland and kidney, and inhibited the activity of vagal gastric nerve. It was further observed that scent of grapefruit oil increased lipolysis, heat production and blood pressure, and suppressed food intake and body weight increase. On the contrary, olfactory stimulation with lavender oil inhibited sympathetic nerve activity and facilitated vagal gastric nerve activity. Further, it suppressed lipolysis, heat production as well as blood pressure, and increased food intake and body weight. The effects of some other essential oils were also observed. Further more, it was observed that olfactory stimulation with scent of ginger, a Chinese medicine, caused an excitation in vagal outflow and a suppresstion in sympathetic outflow. It can be mentioned that these observations are able to give a physiological background to sudy the effects of scents of flowers and plants on human body functions through olfactory system.

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A plant-plant interaction mediated by volatile organic compounds (VOCs) was incidentally found when a potted poplar plant was placed nearby a mechanically damaged conspecific plant. In that case, the plant accumulated higher amounts of polyphenols probably because it perceived VOCs emitted from the wounded plant. Until now, a long list of reports on plant-plant communications mediated by VOCs has been brought about, and it is widely accepted that plants perceive VOCs formed by plants and microbes. However, it is uncertain what kind of perception mechanism is involved in the communication. One possible mechanism for carbonyl compounds is induction of detoxication mechanism plants usually employ against xenobiotics. Upon revealing underlying mechanism of VOCs perception by plants, it might be possible to innovate a novel strategy for sustainable agriculture.

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